1. Field of the Invention
This invention pertains to heavy-duty environmental shaft seals and, more particularly, to those seals which environmentally protect the bearings of sealed bearing rolling cone rock bits.
Such seals are critical in the drilling of wells for the search for and the production of oil. Operating beneath a column of destructively abrasive liquid slurry, a sealed bearing rock bit cannot last much longer than its seals.
As wells are drilled deeper, progressively more unproductive time and labor must be spent retracting the drill pipe to replace a defective rock bit and a substantial portion of such replacements are necessitated by seal failure.
2. Description of the Prior Art
Rock bit bearing seals based on a radially disposed belleville washer, with at least the peripheral lips being encased within an elastomer, are well known in the art. U.S. Pat. No. 3,137,508 teaches the use of this type of seal. A belleville washer behaves as a stiff spring with small deflection in the axial direction.
As wells were drilled ever deeper, and in smaller diameters, it became desirable to rotate the drill faster. The radially disposed belleville seal, due to its relatively large outside diameter, is disadvantaged at higher rotary speeds.
U.S. Pat. No. 3,397,928 shows the use of a common O-ring to seal the bearing of a rolling cone rock bit, minimizing the rubbing velocity between the seal and rock bit surfaces.
To develop sufficient contact pressure against rock bit surfaces, this seal is compressively deformed in its housing gland by an amount which materially shortens its useful life.
The high unit load represented by this contact pressure contributes to abrasive wear of both the O-ring and the gland. This wear serves to reduce the pressure or squeeze of the O-ring as designed.
The elastomeric material of the O-ring, as it is stored in the deformed condition, takes a set or a permanent deformation, materially reducing the contact pressure.
The deformed O-ring, as installed, lacks the compliability of the belleville seal in response to displacements in the relationship of the cutter cone to the journal.